Portable data collection devices are widely used in manufacturing, service and package delivery industries to perform a variety of on-site data collection activities. Such portable data collection devices often include integrated bar code dataform readers adapted to read bar code dataforms affixed to products, product packaging and/or containers in warehouses, retail stores, shipping terminals, etc. for inventory control, tracking, production control and expediting, quality assurance and other purposes. Various bar code dataform readers have been proposed for portable data collection devices including laser scanners and one dimensional (1D) charge coupled device (CCD) imaging assemblies, both of which are capable of reading 1D bar code dataforms, that is, bar codes consisting of a single row of contrasting black bars and white spaces of varying widths. Both laser scanners and CCD imaging assemblies are also capable of reading a "stacked" two dimensional (2D) bar code dataforms such as PDF417, which has row indicator patterns utilized by the reader for vertical synchronization which permit reading successive rows of bar code data.
A two dimensional (2D) imaging based dataform reader has been proposed in U.S. application Ser. No. 08/544,618, filed Oct. 18, 1995 and entitled "Extended Working Range Dataform Reader Including Fuzzy Logic Image Control Circuitry". The 2D dataform reader disclosed in application Ser. No. 08/544,618, which is assigned to the assignee of the present application, includes an imaging assembly having a two dimensional array of photosensors adapted to read 2D bar code dataforms (e.g., PDF417, SuperCode, etc.) with vertical synchronization row indicator patterns as well as matrix dataforms (e.g., MaxiCode, DataMatrix, etc.) which do not include vertical synchronization patterns. The individual photosensors correspond to image picture elements or pixels of the resulting image generated with the photosensors are read out after an exposure period or periods. The 2D dataform reader disclosed in application Ser. No. 08/544,618 utilizes an open loop feedback control system including fuzzy logic circuitry to determine proper exposure time and gain parameters for a camera assembly. Application Ser. No. 08/544,618 is incorporated in its entirety herein by reference.
In U.S. application Ser. No. 08/609,344, a portable data collection device with a color imaging assembly is disclosed. Application Ser. No. 08/609,344 is assigned to the assignee of the present invention and is incorporated in its entirety herein by reference. Application Ser. No. 08/609,344 proposed the use of a color board camera assembly including an RGB (red, green, blue) filter overlying a two dimensional photosensor array. A Y-C signal (Y--luminance signal) and C--chrominance signal) was generated by the color board camera assembly. While the RGB filter permitted color imaging, decoding a dataform image in a captured image frame was problematic. Use of the RGB filter required luminance values corresponding to the Y signal to be adjusted to compensate for changes the intensity of reflected light received by a photosensor depending upon the color of the filter element overlying the photosensor. Application Ser. No. 08/609,344 proposed several methods of compensating for changes in intensity of light directed onto a photosensor when a captured image includes an image of a dataform to be decoded. Even with compensation methods, use of a Y-C signal for dataform decoding has proven less efficient and effective than desired.
What is needed is a color imaging assembly for a portable data collection device that provides the advantage of color imaging with effective and efficient decoding of imaged dataforms.